1. Technical Field
This disclosure relates to a liquid ejection head and an image forming apparatus including the liquid ejection head.
2. Description of the Related Art
Image forming apparatuses are used as printers, facsimile machines, copiers, plotters, or multi-functional devices having two or more of the foregoing capabilities. As one type of image forming apparatus employing a liquid-ejection recording method, an inkjet recording apparatus is known that uses a recording head (liquid ejection head or liquid-droplet ejection head) for ejecting droplets of ink. During image formation, such inkjet-type image forming apparatuses eject droplets of ink or other liquid from the recording head onto a recording medium to form a desired image. The inkjet-type image forming apparatuses fall into two main types: a serial-type image forming apparatus that forms an image by ejecting droplets from the recording head while moving a carriage mounting the recording head in a main scanning direction, and a line-head-type image forming apparatus that forms an image by ejecting droplets from a linear-shaped recording head held stationary in the image forming apparatus.
As one type of the liquid ejection head, a piezoelectric recording head is known that has a channel plate, a diaphragm member, and a piezoelectric member. The channel plate includes separate liquid chambers (also referred to as pressurizing chambers, pressure chambers, separate chambers, liquid pressurizing chambers, or liquid pressure chambers) communicating with respective nozzles for ejecting liquid droplets, fluid resistance portions communicating with the separate liquid chambers, and liquid introducing portions to introduce liquid from a common liquid chamber to supply the liquid to the separate liquid chambers. The diaphragm member has a thick part and a thin part that forms wall faces of the separate liquid chambers, the fluid resistance portions, and the liquid introducing portions. The piezoelectric member deforms vibration areas of the diaphragm member opposing the separate liquid chambers.
For the piezoelectric recording head, there is and has been a trend of the downsizing of the separate liquid chambers to form high-quality images at high speed. As a result, the length of the piezoelectric member (piezoelectric element) in the longitudinal direction is likely to be longer than the length of the separate liquid chamber in the longitudinal direction (i.e., a direction perpendicular to the lateral direction in which the separate liquid chambers are arrayed). Furthermore, in the longitudinal direction, the piezoelectric element may extend to the liquid introducing portion across the fluid resistance portion.
In the case where the diaphragm member has the two-layer structure of thin part and thick part, if the length of the piezoelectric element in the longitudinal direction is relatively great as described above, areas of the diaphragm member forming wall faces of the fluid resistance portions and the liquid introducing portions are preferably made of the thin part to prevent interference of the diaphragm member with the piezoelectric element.
However, if the wall faces of the liquid introducing portions and the fluid resistance portion are formed of the thin part, the thin part may vibrate due to fluctuations in pressure on ejection of droplets, thus creating a natural vibration having a mode differing from the natural vibration mode of the separate liquid chamber. As a result, the control performance of droplet ejection may decrease, thus degrading the ejection performance.
Hence, for example, JP2007-144706-A1 proposes a liquid ejection head in which each fluid resistance portion is bent from a corresponding separate liquid chamber so as to overlap a thick part of the diaphragm member.
Additionally, JP2007-176153 proposes a liquid ejection head in which, in the longitudinal direction of the liquid pressure chamber, the length of the pressure generator (piezoelectric element) is greater than the length of the liquid pressure chamber, and an end portion of the pressure generator proximal to a supply channel is disposed at a position opposing an area of the diaphragm member facing the liquid pressure chamber without opposing another area of the diaphragm member facing the supply channel.
However, in the configuration described in JP2007-144706-A1, in a case where the piezoelectric member extends to the liquid introducing portion disposed upstream from the fluid resistance portion, natural vibration may occur in an area of the diaphragm member forming a wall face of the liquid introducing portion. Further, in a case where the channel plate is formed by etching a silicon substrate, the configuration of the fluid resistance portion described in JP2007-144706-A1 cannot be formed.
In the configuration described in JP2007-176153, a thick portion of the diaphragm member is bonded to the piezoelectric element at a position offset to one side of the piezoelectric element. However, if the thick portion of the diaphragm member is disposed in the middle of the piezoelectric element, the diaphragm member interferes with the piezoelectric element unless an area of the diaphragm member forming a wall face of each fluid resistance portion is formed of the thin part. Therefore, the above-described challenge remains unsolved that natural vibration occurs in other areas of the thin part except for the vibration area opposing the liquid pressure chamber.